My Lumia 520 got an update to Windows 10 Mobile. I started upgrading but the battery drained out. Now whenever I start the phone, I see moving gears on the screen but after some time the phone restarts and it happens again. The battery is fully charged but it happens all the time.

I'm stuck, what should I do? Also my phone's power button doesn't work so I can't hard reset it.

3 Answers
3

Run NSU and this window will pop up. Then click "My device does not boot up"

Now connect the phone that has been stuck at spinning gears via USB cable (make sure its fully charged) and click continue.

After connecting the phone, this will show up (refer screenshot). Now press and hold the power and the volume down button until the
phone vibrates. Your PC will detect a new hardware and will install
the required drivers if needed. Then click Ok.

NSU will take over from here and will reflash your phone with a hefty 1.2GB of firmware download from its server. Let it finish and
then you're done.

It always happened to me to no matter what windows version it was and recently it happened while upgrading to windows 10 too the only solution that worked for me then and now is to remove the memory card and reset the phone using the Volume Down key + Power button after which the upgrade will continue so try doing that and you wont get stuck at rotating gear remember to put back the memory card in after its done updating. (Remember to wait for a while after removing memory card say about 2 min at the gears rotation screen and then you'll see it updating)

In the device recovery tool, select Lumia and select My phone is not detected.

The tool will automatically find your device.

You will be having Install software instead of the reinstall as shown above. Click on that icon. The next screen will ask you for a reason. Provide one and click next. You will see the following screen.

Click on Continue.

Now it will download about 1.6GB-2GB for WP8.1 and 2.7GB for Windows 10 Mobile of files from the internet. Don't worry if it gets broken in the middle just hit retry it will resume from where it left.

Then the new OS will be installed on the phone.

Note: For phone that came with Windows phone 8.1 only Windows Phone 8.1 will be installed and not Windows 10. You can update to Windows 10 later.